Laboratory Skills and Data Analysis
What you must understand
Know safe practice: correct use of goggles, fume hoods, and waste containers; proper handling of acids, bases, and flammable solvents; and appropriate response to spills and glassware breakage. Select apparatus by precision: graduated cylinders versus burettes versus volumetric flasks versus analytical balances. Distinguish accuracy from precision, random from systematic error, and identify sources of each. Perform unit conversions and significant-figure handling, propagate uncertainty, and interpret graphs by slope and intercept. Understand calibration curves, titration technique, and the purpose of controls and replicates.
Traps to watch for
- Confusing accuracy with precision; a consistently high reading is precise but inaccurate.
- Reading a meniscus at eye level incorrectly or ignoring parallax.
- Using a volumetric flask for storage or heating, or a graduated cylinder for precise titration volumes.
- Reporting more significant figures than the instrument supports.
- Treating a systematic error as something averaging replicates will fix; it will not.
Worked example
A balance consistently reads 0.05 g high across replicate weighings. The measurements are precise but inaccurate, indicating systematic error. Averaging more trials will not remove it; recalibrating or zeroing the balance will. By contrast, fluctuating readings around a true value indicate random error, which averaging can reduce.
Rule of thumb
Precision is reproducibility; accuracy is closeness to the true value. Fix systematic error by calibration, not by more replicates.